L. Laakso1, A. Hirsikko1, T. Grönholm1, M. Kulmala1, A. Luts2, and T.-E. Parts21Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland2Institute of Environmental Physics, University of Tartu, Ülikooli 18, 50090 Tartu, EstoniaAbstract. In this study, we measured the mobility distributions of cluster and intermediate ions with an ion spectrometer near a waterfall. We observed that the concentration of negative 1.5–10 nm ions was one-hundred fold higher than a reference point 100 m away from the waterfall. Also, the concentration of positive intermediate ions was found to be higher than that at the reference point by a factor of ten. This difference was observed only at the smallest sizes; above 10 nm the difference was insignificant.